The present invention relates to a constant velocity joint of tripod type, which is disposed between rotating shafts connected at a joint angle with each other in a drive axle of, for example, an automobile, for transmitting a rotational torque.
Tripod type constant velocity joints are one of a number of types of constant velocity joints used in drive axles of, for example, automobiles. For example, Japanese Laid Open Patent Application Nos. S63(1988)-186036 and S62(1987)-233522 disclose a tripod type constant velocity joint 1, as shown in FIGS. 15 and 16. This constant velocity joint 1 is provided with a hollow cylindrical housing 3 which is secured to an end of a first rotating shaft 2 serving as a drive shaft or the like on the differential gear side, and a tripod 5 which is secured to an end of a second rotating shaft 4 serving as driven shaft or the like on the wheel side. Grooves 6 are formed at three locations on the internal face of the housing 3 at an even spacing in the circumferential direction and extend outwardly in the radial direction of the housing 3 from said internal face.
On the other hand, the tripod 5 secured at one end of the second rotating shaft 4 comprises a unified form of a boss 7 for supporting the tripod 5 at one end of the second rotating shaft 4, and trunnions 8 formed on three locations at equal spacing around the boss 7 in the circumferential direction. Around the respective trunnions 8 each of which is cylindrically formed, rollers 9 are rotatably supported through a needle bearing 10, while allowing the rollers 9 to be displaced in the axial direction by certain distances. A joint is provided by engaging the respective rollers 9 with the grooves 6 on an inner face of the housing 3. Respective pairs of side faces 11, on which each of the above grooves 6 is provided, are formed to circular recesses. Accordingly, each of the rollers 9 is rotatably and pivotably supported between the respective pairs of the side faces 11.
When the constant velocity joint 1 as described above is used, for example, the first rotational shaft 2 is rotated. The rotational force of the first rotational shaft 2 is, from the housing 3, through the roller 9, the needle bearing 10 and the trunnion 8, transmitted to the boss 7 of the tripod 5, thereby rotating the second rotational shaft 4 the end of which is fixed to the boss 7. Further, if a central axis of the first rotational shaft 2 is not aligned with that of the second rotational shaft 4 (namely, a joint angle is not zero in the constant velocity joint 1), each of the trunnion 8 displaces relative to the side face 11 of each of the grooves 6 to move around the tripod 5, as shown in FIGS. 15 and 16. At this time, the rollers 9 supported at the ends of the trunnions 8 move along the axial directions of the trunnions 8, respectively, while rolling on the side faces 11 of the grooves 6, respectively. Such movements ensure that a constant velocity between the first and second rotational shafts 2 and 4 is achieved, as is well known.
If the first and second rotational shafts 2 and 4 are rotated with the joint angle present, in the case of the constant velocity joint 1 which is constructed and operated as described above, each of the rollers 9 moves with complexity. For example, each of the rollers 9 moves in the axial direction of the housing 3 along each of the side faces 11, while the orientations of the rollers 9 are being changed and further the rollers 9 displace in the axial direction of the trunnion 8. Such complex movements of the rollers 9 cannot cause a relative movement between a peripheral outside face of each of the rollers 9 and each of the side faces 11 to be smoothly effected. Thus, a relatively large friction occurs between the faces. As a result, in the constant velocity joint 1 of FIGS. 15 and 16, three-directional axial forces occurs per one rotation. It is known that an adverse oscillation referred to as xe2x80x9cshudderxe2x80x9d may occur in some cases, if a large torque is transmitted with a relatively large joint angle present.
To prevent any oscillation from occurring due to the above cause, for example, Japanese Laid-Open Patent Application No. H3(1991)-172619 discloses a structure shown in FIG. 17 and Japanese Publication Patent Application No. H4(1992)-503554 discloses structures shown in FIGS. 18 and 19.
In the case of a structure shown in FIG. 17, since movement of an outer roller 16 and an inner roller 12 in an axial direction of a trunnion 8 is limited, when a constant velocity joint of the structure rotates at a joint angle, a large amount of frictional resistance is generated due to any axial displacement between the inner cylindrical face of the inner roller 12 and the spherical trunnion 8, applying a pressing force onto the inner roller 12 and the outer roller 16, and then producing a frictional force preventing the inner roller 12 and the outer roller 16 to be rotated with each other.
Moreover, since an area of contact between the inner cylindrical face of the inner roller 12 and the spherical trunnion 8 is small, when torque is transmitted through the contact area during rotation at a joint angle, it is susceptible to wear and damage.
In the case of the joint shown in FIG. 18, the number of components is increased since an element is provided for determining the location of an inner roller relative to a partially spherical trunnion, and also the machining process is relatively complicated.
In the case of the joint shown in FIG. 19, since the inner roller are deformed in assembling, a wall thickness of an inner roller is in part reduced causing it to be relatively weak.
The object of the present invention is to provide a tripod type constant velocity joint which is both highly strong and durable, and which can maintain a low axial force and low shudder when transmitting torque at an angle.
In order to attain the above object, a constant velocity joint of tripod type according to the first aspect of the invention comprises a cylindrical hollow housing defining an opening at one end. The housing is secured at its opposite end to a first rotating shaft such that a central axis of the housing is aligned with that of the first rotating shaft. An inner face of the housing is provided with three guide grooves extending in an axial direction of the housing and being spaced apart equally in a circumferential direction. Each groove has a pair of side faces opposed to each other and extends in the axial direction with a bottom portion connected between the side faces. A tripod is provided at an angle normal to a second rotating shaft and secured to one end of the second rotating shaft. The tripod has three trunnions positioned in the grooves. The trunnions are spaced apart equally in a circumferential direction and secured equally to the second rotating shaft at an angle normal. Respective inner rollers are mounted to outside end portions of respective trunnions and respective outer rollers are mounted on the outer faces of inner rollers through a needle bearing. The outer faces of the outer rollers are shaped so as to allow movement only in an axial direction of the grooves. Each of the trunnions has a generally spherical outer face, and each of the inner rollers has a generally spherical outer face. Respective generally spherical outer faces of the inner rollers have approximately the same dimensions as respective generally spherical outer faces of the trunnions such that respective inner rollers may rotate and pivot freely on respective outer faces of respective outer face of respective trunnions.
The constant velocity joint of tripod type is characterized in that, on each outer face of each trunnion, there is provided a partially cylindrical area inclined relative to a trunnion centerline (Q). The trunnion centerline (Q) means a line passing through a center (O) of the generally spherical outer face of the trunnion, perpendicular to a trunnion axis (M) of the trunnion, and being on a face including the trunnion axis (M) and a portion in contact with the inner roller, with a joint angle being zero. The trunnion axis (M) means an axis passing through the center (O) of the generally spherical outer face of the trunnion, and perpendicular to the second rotating shaft.
In order to attain the above object, a constant velocity joint of tripod type according to the second aspect of the invention is characterized in that a diameter (d) of each partially cylindrical area provided on each outer face of each trunnion is related to an inner diameter (D) of each inner joint end surface of each inner roller in accordance with the following formula:
(d) less than (D)
and
5xc2x0xe2x89xa6angle(xcex8),
wherein the angle (xcex8) is an angle of a line connecting between the center (O) of the trunnion and a farthest point (P), relative to the trunnion centerline (Q). An intersection line (13a) being an edge line of the partially cylindrical area at an inner side of a joint. The farthest point (P) being on a location where the intersection line (13a) is farthest from a center of a joint, on the outer face of the trunnion.
The present invention can provide a tripod type constant velocity joint which is both highly strong and durable, and which can maintain a low axial force and low shudder when transmitting torque at a joint angle.
These and other objects and advantages of the present invention will be more apparent from the following detailed description and drawings in which: